Studies of concurrent operation within a computer system and of the representation of parallelism in a programming language have yielded a new form of program representation, known as data flow. A data-flow language is data-driven; that is, each instruction is enabled for execution just when each required operand has been supplied by the execution of a predecessor instruction. Data-flow representations for programs have been described by Karp and Miller [8], Rodriguez [11], Adams [1], Dennis and Fosseen [5], Bahrs [2], Kosinski [9, 10], and Dennis [4]. The use of such languages in a processor is disclosed in Dennis [3]. Details of the above designated references are given below.